Internal ventilating system for a rotating electrical machine such as a motor vehicle alternator

ABSTRACT

The invention concerns a rotating electrical machine, comprising inside a housing, a fixedly mounted stator and a rotor rotatably mounted in the stator, the ventilating system including in particular at least one ventilator integral with the rotor and capable of generating a cooling air stream inside the housing, radial air intake orifices ( 20 ) arranged in the housing, and cooling air discharge ports ( 22 ) arranged in said housing in a ring opposite the periphery of the ventilator and mutually separated by fins ( 24 ) stiffening the housing in the port region. The system is characterized in that the angle of inclination of the fins ( 24 ) relative to the tangent perpendicular to the radial direction (R) ranges between 38° and 52°. The invention is for use for motor vehicle alternators.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention concerns an internal ventilating system for a rotatingelectrical machine of the type that includes, within a housing, a statorfixed-mounted in the housing and a rotor rotary-mounted in the stator;the ventilation system includes in particular at least one ventilatorintegrated with the rotor and capable of generating a cooling air streamwithin the housing, radial air intake orifices arranged in the housingand cooling air discharge ports arranged in said housing in a ringopposite the periphery of the ventilator and separated from each otherby fins stiffening the housing in the area of the ports. The inventionalso concerns a rotating electrical machine that includes such aventilation system.

2. Background Art

It has been shown that, to minimize the pressure losses caused by thefins and the noise due to the cooling fluid flows (air in this case), itis advantageous to incline them according to the direction of the airflow that must be discharged. The necessity to combine ventilator andhousing is a serious disadvantage.

SUMMARY OF INVENTION

The purpose of this invention is to offer a ventilation system of thetype described above, which reduces this disadvantage.

To achieve this purpose, the ventilation system in the invention ischaracterized in that the angle of inclination of the fins in relationto the tangent is between 38° and 52°.

Surprisingly, it has been demonstrated that such a range of angles issuitable for a large number of ventilator-housing combinations, whileproviding low pressure losses and a reduction in noise. Thus, for eachventilator-housing combination, we calculate the angle of inclinationand propose a range.

According to one characteristics of the invention, it is advantageous tochoose the angle at a value of 45°.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be understood better, and other purposes,characteristics, details and advantages of the invention will appearmore clearly in the explanatory description that follows, which refersto the attached schematic drawings that are provided only as an exampleillustrating one method for making the invention, in which:

FIG. 1 is an axial cross section of an alternator according to the stateof the art;

FIG. 2 is a simplified schematic view of a ventilation system accordingto the invention, showing a ventilator and cooling air discharge ports;

FIG. 3 is a perspective of a front main bearing equipped withventilation ports according to the invention; and

FIG. 4 illustrates another advantageous characteristic of theventilation system according to the invention;

FIG. 5 is a radial view of the interior of a flat stator.

DETAILED DESCRIPTION

Referring to FIG. 1, we will first describe the general structure of aventilation system for a rotating electrical machine, in this case analternator for an automobile, to place the invention in its context.This type of alternator is described, for example, in document FR-A-2602 925, to which we will refer for more explanations.

On this figure, reference 1 designates a perforated alternator housingin general rotating form, which coaxially surrounds a stator 4 equippedwith windings 5 within which is rotary-mounted a rotor 6 of the typewith prongs that includes a shaft 7 supported by the housing throughfront main bearing 9 and rear main bearing 10. The rotor is composed oftwo polar parts, the front one 12 and rear one 13, and a winding 14.Each polar part 12, 13 carries on its plate part a ventilator, a frontventilator 15 and rear ventilator 16. The ventilators are integrated inrotation with their respective support polar part. The stator 4 iscarried in the inside by housing 1.

As shown schematically on the figure, each ventilator carries on itsoutside open face a number of ventilation blades 18.

Housing 1 is formed of two hollow parts called respectively front mainbearing 19 and rear main bearing 21.

These main bearings are attached together, for example, with a screw 26and each contains a part with a generally transversal orientationconnected through a connection zone to a ring with an axial orientation.The main bearings carry in the center, toward their transversal part,the bearings 9, 10, and the front main bearing is adjacent to the drivepulley of the alternator, and the rear main bearing is adjacent to therectifier bridge (not referenced) carried by the alternator.

The transversal sections of the main bearings are equipped with axialair intake orifices 20. The ring of the main bearings extends to theoutside periphery of the bearings and carries the stator 4 on the insidemore specifically, the body presented by the stator to carry thewindings 5. This ring is equipped with orifices 22 called ports.

The ports 22 are axially oblong and also affect the external peripheryof the transversal section of the main bearing in question. The ports 22extend on either side of the body of the stator 4 and are locatedoutside the projecting parts, called chignon, of the windings 5 and theventilators. The ports 22 thus contain a section with an axialorientation, called the axial orifice, that only affects the ring of themain bearing.

The axial orifices have an axial length equal to the height of acylindrical portion of the ring delimited by a first circlecorresponding to the bottom of the ports adjacent to the body of thestator and by another circle corresponding to the edge of the axialorifices of the ports. FIG. 3 shows a perspective of the ports 22delimited by fins 24.

The ventilators are configured to create a cooling air flow, thecomponents of which are indicated by arrows, sucking in ambient airthrough intake axial orifices 20. A portion of the cooling air indicatedby arrow F is discharged through the ports 22.

The invention concerns the internal ventilation system that essentiallyincludes a ventilator 15 or 16 and the ports 22 to discharge the airflow created by the ventilator and illustrated by arrow F.

We will describe the invention below by referring to FIGS. 2 and 3. Onthese figures, as on FIG. 1, the ventilator is designated by 16, theventilator blades by 18, and the ventilation ports by 22.

As we see on FIG. 3, on which the section of the housing that has theports 22 is a front main bearing; the ports 22 are obtained by placingfins 24 in the appropriate orifices in the peripheral surface of themain bearing; the fins extend parallel to the axis of the alternator andare inclined in an angle predetermined in relation to the radialdirection R. The function of the fins 24 is to mechanically stiffen themain bearing.

In accordance with the invention, the fins 24 present an angle ofinclination of between 38° and 52°, and preferably 45° in relation tothe tangent perpendicular to the radial direction. In other words, theangle of inclination in relation to the radial direction R is between(90°-38°) and (90°-52°).

Despite the general opinion that the fins must have an inclination thatis substantially parallel to the direction of the cooling air flow thatmust be discharged through the ports, for each ventilator/housing ormain bearing combination, to avoid significant pressure losses, it hasbeen demonstrated that when inclinations in the range of 38° to 52°cited above are selected, good ventilator/main bearing compatibility isretained in a large number of such ventilator/main bearing combinations,with relatively low pressure losses and reduced air flows. Thus, theventilation system is less noisy.

With respect to the fabrication of the ports 22 and the fins thatseparate them, it should be noted that the radial orifice factor of theports must be at least 40% to the extent that an increase in the radialorifice surface significantly increases the cooling efficiency of theventilators, i.e. particularly electronic components in the rear mainbearing of the alternator and the windings.

In order to increase the performance of the ventilation system, weincrease the circumference of the axial orifices of the ports 22 so thatthe surface of the axial orifices represents at least 40% of the surfaceof the aforementioned cylindrical section of the ring.

FIG. 4 shows another measurement that optimizes the cooling of thealternator. In effect, this figure illustrates that the ventilatorblades should not overlap by more than a third, i.e., the distance 1 oftheir cord length L, the axial orifices as indicated in 20 on FIG. 1 ofthe housing or of the front or rear main bearings. In other terms, theoutside diameter of the axial orifices must be chosen on the basis ofthe interior and exterior diameters of the ventilator.

It is advantageous, to obtain optimized ventilation, for the fins to bearranged so that they are angularly separated by a distance D=F.360°/Nin which N=the number of notches of the stator, and F is a multipliercoefficient that is determined as a function of the mechanicalconfiguration of the electrical machine, by serial calculation.

Thus, for example,

-   -   if N=36 notches, then 1.360°/36=10°. The fins are, thus,        angularly separated by 10° or a multiple of 10°;    -   if N=48 notches, then 2.360°/48=15°. The fins are angularly        separated by 7.5° or a multiple of 7.5°;    -   if N=96 notches, then 3.360°/96=11.25°. The fins are angularly        separated by 3.75° or a multiple of 3.75°.

Thus, as shown on FIG. 5, this configuration obtains an optimizedventilation thanks to a reduction in load losses in front of thechignons of the winding 5 rolled in grooves 32 of the stator 4.

In effect, the winding density of the front chignon 30 and the rearchignon 31 (partially shown on FIG. 5 for reasons of clarity) which exitaxially from the stator 4 present a maximum density above the grooves 32and form an obstacle for the discharge of the air through the radialports 22. Thus, according to the invention, the fins 24 are arranged tocoincide angularly with these high density winding zones and not createadditional obstacles in front of the air passages 34 above the teeth 33of the stator. For this purpose, the fins 24 are radially aligned withthe grooves 32 of the stator.

It is advantageous for the fins to be radially aligned on only a portionof all the grooves 32 of the stator. The pitch of the fins can be amultiple of the pitch of the grooves/teeth of the stator.

According to another method of fabrication, the fins can radiallyoverlay the grooves 32 of the stator with a random pitch 35.

It is advantageous for at least 70% of the fins to be radially alignedwith the grooves of the stator.

1. Internal ventilation system of a rotating electric machine such as anautomobile alternator, of the type that consists of, within a housing, afixed-mounted stator in the housing and a rotary-mounted rotor in thestator; the ventilation system contains at least one ventilatorintegrated with the rotor which is capable of creating a cooling airstream within the housing, air intake axial orifices (20) arranged inthe housing and cooling air discharge ports arranged in said housing ina ring with respect to the periphery of the ventilator and separatedfrom each other by fins (24) stiffening the housing in the area of theradial ports (22), characterized in that the angle of inclination of thefins (24) in relation to the tangent perpendicular to the radialdirection (R) is between 38° and 52°, and in that the radial ports (22)have an axial oriented section, called the axial orifice, that axiallyaffects only the axial oriented ring and belongs to a cylindricalportion, and characterized in that the surface of the axial orificesrepresents at least 40% of the surface of the cylindrical section. 2.Ventilation system in accordance with claim 1, characterized in that theangle of inclination of the stiffening fins (24) is 45°.
 3. Ventilationsystem in accordance with one of claims 1 to 2, characterized in thatthe angular distance between the air discharge radial fins (24) is equalto F.360°/N in which N is the number of notches present in the statorand F is a multiplier coefficient.
 4. Ventilation system in accordancewith the preceding claim, characterized in that the fins (24) areradially aligned with the grooves (32) of the stator.
 5. Ventilationsystem in accordance with claim 3, characterized in that at least 70% ofthe fins (24) are radially aligned with the grooves (32) of the stator.6. Ventilation system in accordance with claim 3, characterized in thatthe pitch of the fins (24) is a multiple of the pitch of the grooves(32) of the stator.
 7. Ventilation system in accordance with claim 1,characterized in that the part of the cord length (L) of the blades (18)of a ventilator (16) overlapping the axial orifices (20) of the housingmust be less than or equal to one third.
 8. Rotating electrical machinesuch as an alternator, particularly for an automobile, characterized inthat it includes a ventilation system in accordance with one of claims 1to 7.